Create new document in the document library

Hi, I want to create and upload a new entry to my KB library based on text messages from the chat. I am following this documentation, but I cannot get it to work. From what I see this is built for uploading documents whereas what I want is to create a new document from text and then insert it into the KB.
https://developer.voiceflow.com/reference/post_v3alpha-knowledge-base-docs-upload